This invention relates to improvements in a valve timing control system for an internal combustion engine, arranged to variably control opening and closing timings of engine valves such as an intake valve and an exhaust valve of the internal combustion engine in accordance with an engine operating condition, and in a method for assembling the valve timing control system.
Hitherto, various types of valve timing control systems for internal combustion engines are proposed and put into practical use. One of such valve timing control system is of a so-called vane type and disclosed in Japanese Patent No. 3081191. Briefly, this valve timing control system includes a housing having a cylindrical housing main body. Opposite openings of the housing main body are respectively closed with a front cover and a rear cover. The housing main body, the front cover and the rear cover are joined with each other as a single member through a plurality of bolts.
This housing accommodates therein a vane member fixed to an end section of a cam shaft and rotatable inside the housing. The housing further includes three shoes each of which is generally trapezoidal (in section) and formed to radially inwardly project from the inner peripheral surface of the housing. The vane member includes three vanes each of which defines a timing-advancing oil chamber and a timing-retarding oil chamber between it and the adjacent shoes.
The above-mentioned rear plate is provided at its outer peripheral side with a sprocket as a single member, so that rotational force of a crankshaft is transmitted to the sprocket through a timing chain.
The above-mentioned one vane is formed with a hole for slidable movement which hole extends in an axial direction of the one vane. A lock pin is disposed slidably movable forward and rearward in the hole. The above-mentioned rear plate is formed at its inside surface with a lock hole to or from which the above-mentioned lock pin is engaged or disengaged.
Oil pressure discharged from a pump rotationally drivable in right and reverse directions is selectively supplied to any one of the above-mentioned timing-advancing oil chamber and the timing-retarding oil chamber in accordance with the engine operating condition. Thus supplied oil pressure drives the vane member in the right and reverse directions thereby varying relative rotational phases of a timing pulley (or the sprocket) and the cam shaft, so that the opening and closing timings of the intake valve can be variably controlled.
During engine stopping, the above-mentioned lock pin is fitted into the lock hole so as to retain the relative rotational angular position of the vane member to the above-mentioned housing at an optimum position for engine starting. This prevents the vane member from flattering in a peripheral direction owing to so-called alternating torque so that a good restarting ability can be secured.